Today's, vehicle air conditioning systems working, with the refrigerant R134a, exhibit a pressure sensor on the “high pressure side” after the compressor usually for monitoring the operating pressure and for control. If the operating pressure exceeds a given maximum pressure, a regulation intervenes, which down-regulates the operating pressure e.g. by switching the compressor off into a “normal-pressure range”.
Due to various reasons CO2 will be used as the refrigerant in future motor vehicle air conditioning systems. For the regulation of a “CO2-Refrigerant cycle” the refrigerant pressure and additionally the refrigerant temperature are needed after the compressor as controlling signals. In “CO2-Air Conditioning Systems” the refrigerant pressure and the refrigerant temperature after the compressor are physical dimensions, which should be measured independently. For the monitoring of the refrigerant pressure and the refrigerant temperature one can plan a pressure sensor and additionally a temperature sensor. The use of two separate sensors is unfavorable as they have to be mounted separately to the air conditioning system in separate housings, which can lead to additional leakage problems.
An arrangement for measuring a pressure and a temperature is disclosed in U.S. Pat. No. 6,212,946 B1. The pressure sensor and the temperature sensor are secured in a common housing. In order to introduce a fluid that is under pressure, a neck part is secured to the housing and an adapter is joined both to a substrate and to the neck part via adhesive seals that decouple mechanical stress from the pressure and temperature detectors.
Furthermore a sensor arrangement for measuring a pressure and a temperature is disclosed in FR 2691802. The sensor arrangement has a body with a leak-proof tube attached to it. Inside the tube is a temperature probe or thermocouple with a cable to external electronics. On top of the body is a protective cap. The protective cap encompasses a compartment comprising a pressure transducer and associated electronics. Holes in the body allow fluid to pass to the pressure transducer.
This kind of sensor arrangements for detecting the pressure and temperature in a fluid are very complicated to produce. Furthermore, in an air-conditioning system using a CO2 stream, the sensor arrangement needs to be able to measure pressures up to 200 bar and temperatures in a range of −40° C. to +180° C. In such systems the sensor arrangement should be fully hermetic. With elastic and adhesive materials such as elastomers it is nearly impossible to seal CO2 reliably.
In fuel injections systems, the viscosity of the fuel to be injected is dependent of the temperature of the fuel. If the temperature increases, the viscosity will decrease. Consequently, with the same pressure, more fuel will be injected. This is an undesired effect that has to be compensated. To enable a controller to inject the required amount of fuel, there is a need to have a combined temperature pressure sensor, which is able to measure simultaneously temperature and pressures up to 250 Bar and higher.